The present invention relates to a device capable of signalling the inflating condition in the tires; the device comprises an external covering capable of rotating together with a threaded body used for screwing the device on the body of a standard inflating valve, a chamber defined inside the threaded body, an element sensible to the pressure existing in the chamber, a member which can be deformed by the pressure considering the temperature and a system capable of signalling the position of the deformable member.
U.S. Pat. No. 5,694,969 relates to a device for inflating a tire of a wheel. A pressure relief tire valve for inflating a tire wheel assembly has a tire inflation valve body having a chamber therein with openings through the top and bottom ends thereof and having a relief opening formed in the tire valve body. An inflation valve having a spring loaded central core to allow to pass inward is located in the tire valve body adjacent the tire inflation valve body top end for inflating the tire there through. An over pressure valve is located in the tire valve body for releasing air from the tire when the air pressure in the tire exceeds a predetermined level. The over pressure valve has a valve seat and valve element biased against the valve element by a compression for maintaining the valve element in a closed position until the predetermined air pressure is reached in the tire and to allow the valve element to open to release air through the valve body relief opening when the air pressure in the tire and to allow the valve element to open to release air through the valve body relief opening when the air pressure in the tire exceeds the predetermined pressure. A heat variable bellows supports the compression spring and is responsive to changes in temperature of the air in the tire so that the over pressure valve can prevent over inflating the tire as well as loss of tire pressure upon an increase of air pressure in the tire from an increase in temperature of the air in the tire.
U.S. Pat. No. 3,451,418 (Nakagawa Shunshi et Al.) [D1] discloses a device for indicating the interior pressure of a pneumatic tire; the device comprises an hollow body and inflatable means disposed in the hollow body; means being provided for maintaining the air valve of the pneumatic tire in a normally open position. The interior pressure of the pneumatic tire is in communication with the interior of the inflatable means. In addition, the device is also fitted with means capable of automatically indicating the interior pressure of the pneumatic tire at any given moment of time. The device is secured to the air valve of the pneumatic tire and is capable of having compressed air charged directly therethrough for inflating the pneumatic tire.
The device further comprises means for automatically closing the air valve of the pneumatic tire when the interior pressure thereof has dropped below a predetermined value.
U.S. Pat. No. 2,866,432 (Laurie) [D2] relates to a tire pressure indicating device.
A tire pressure indicator acts in combination with a valve stem having a tire valve therein. The indicator comprises a body having an open ended chamber adjacent one end thereof; a snap diaphragm is normally bowed outward, and extends across the open end of the chamber; indicator adjusting means are further provided for adjustably predetermining the normal arc of bowing of the diaphragm.
The tire pressure indicator is also fitted with sealing means to seal the diaphragm to the chamber in air-tight relation to thereby close the open end of the chamber to the atmosphere; the diaphragm being movable between an inward depressed position and the normally bowed outward position with an audible click action.
The other end of the body has a threaded bore in communication with the chamber and adapted to be detachably secured to the threaded end of the tire valve stem; a slidable plunger stem extends through the chamber and bore, the plunger having one end adapt to contact the inner surface of the diaphragm, while the other end of the plunger stem is positioned to contact the valve stem of the tire valve when the diaphragm is moved to the depressed position to thereby release the tire air pressure to within the bore and chamber behind the diaphragm.
In these and other documents of prior art the following features are not shown:
a rod [of a plunger] having two sections with two external diameters if the difference between the tire pressure and the atmospheric pressure exceeds at least one pre-established threshold value;
an element with variable geometrical configuration which closes a housing, the geometrical configuration of the element depending on the difference between the tire pressure and the atmospheric pressure; the element presenting a first geometrical configuration when the atmospheric pressure acts on the housing and the tire pressure is higher than the highest pre-established threshold value, and a second geometrical configuration when the tire pressure is below the lowest pre-established threshold value;
a sealing member separating a first chamber, defined under the plunger, from a second chamber defined over the plunger;
a first duct connecting the housing to the first chamber, which, in its turn, is connected to the atmosphere through a second duct, a channel and a groove;
a third chamber being separated from the first chamber when the plunger is found in the first limit stop;
ducts and a bistable valve fitted with a double closing device, acted by the element with variable geometrical configuration, for connecting the second chamber to the air tube, so that, when the element with variable geometrical configuration is found in the first configuration, the bistable valve can reach the first position of stability and the plunger can be found in the first limit stop, and, vice versa, for connecting the first and second chambers to each other, and for joining said chambers with the atmosphere through the second duct, the channel and the groove, when the element is found in the second configuration, and consequently, the bistable valve reaches the second position of stability;
when the pressure falls below the lowest pre-established threshold value, the element with variable geometrical configuration for allowing the bistable valve fitted with a double closing device to reach the second position of stability and close the connection between a third duct and the second chamber through a channel and a fourth duct and to open the connection between the second chamber and the housing, in its turn jointed to the atmosphere through said channel and the third duct.
The technical effect of these distinguishing features is that the plunger is actuated by the difference in pressure between the first chamber defined under the plunger and the second chamber defined over the plunger. The pressure in this first and second chamber is established via a bistable valve actuated by the element with variable geometrical configuration which works like a spring diaphragm having two possible configuration depending on the pressure of the tire in relation of a threshold value.
Contrary to this method, the plunger of D1 works like a piston actuated by the tire pressure which compresses a mechanical spring.
The present invention solves the problem of providing different means which actuate the plunger depending on the tire pressure.
Although the Document D2 discloses a device capable of signalling the tire pressure comprising a spring diaphragm similar to the element with variable geometrical configuration of the present invention for indicating the tire pressure, this spring diaphragm indicates the tire pressure simply by its configuration, without engaging other members of the device.
Thus, even if the skilled person would use the spring diaphragm of D2 in the device of D1, there is no indication to link this spring diaphragm with a bistable valve in order to establish different pressures in a first and second chamber actuating the plunger depending on a threshold value of the tire pressure.
This and other documents of prior art do not regard a device for signalling the inflating state in the tires, but an assembly limiting pressure in the case of an excessive increase of the air tube temperature.
The present invention, as claimed, solves the problem of creating a device capable of signalling the inflating condition in the tires. The results obtained by means of the present invention mainly consist in the fact that the function of checking and automatically preventing the escape of air from the tire continues to be effected by the self-closing core of the inflating valve also in presence of the device, which is, therefore, used only for signalling if the tire pressure is correct or not, without introducing the risk of the tire being deflated in case the same device presents an escape.
The advantages offered by the invention consist in the fact that the tire pressure is indicated considering at least one threshold value; above said thresh old value the device signals the normal inflating state of the tire, while the same device signals the non correct inflating state when the tire pressure is below the same threshold value or another pre-established value lower than the previous threshold value; a temperature-sensing element allows to consider the temperature for defining the threshold values while a signalling system indicates if the tire inflating condition is correct or not.